1. Technical Field
The present invention relates to semiconductor devices having a so-called source-body-tie structure in which a body region and a source region are connected to each other, and methods for manufacturing the same.
2. Related Art
Research and development are being made in recent years on insulated gate type transistors which are provided in a semiconductor layer (SOI layer: Silicon On Insulator layer) provided on a dielectric layer as devices that can realize lower power consumption and high-speed operation, compared to the case where transistors are formed in a semiconductor layer in a bulk state. Among insulated gate type field effect transistors provided in such a SOI layer, there are those having a source-body-tie structure in which a source region and a body region are connected to each other. FIG. 8 shows a plan view of a semiconductor device including a MOS transistor having an exemplary conventional source-body-tie structure, FIG. 9(A) shows a cross-sectional view taken along lines A—A in FIG. 8, and FIG. 9(B) shows a cross-sectional view taken along lines B—B in FIG. 8. As an example of a conventional semiconductor device, a device having an n-channel type MOS transistor provided on a SOI layer is indicated. The exemplary conventional semiconductor device includes a gate dielectric layer 120 provided on a semiconductor layer 110 and a gate electrode 122. A source region 126a and a drain region 126b which are composed of n-type high concentration impurity regions are provided in the semiconductor layer 110. Further, the source region 126a is divided by a body contact region 130 into plural areas. The body contact region 130 is composed of a p-type impurity region, and is provided in a manner to connect to a body region 112.
The source region 126a and the drain region 126b are provided with contact sections 140, respectively. Holes that are generated by impact ionization below the gate electrode 122 would be absorbed by the contact sections 140 through the body contact region 130. In a MOS transistor having a source-body-tie structure, holes generated by impact ionization can be absorbed in this manner, and therefore a semiconductor device having a reduced substrate floating effect can be provided.
In the exemplary conventional semiconductor device described above, impact ions generated below the gate electrode 122 are absorbed by the contact sections 140 through the body region 112 and the body contact region 130. In other words, holes generated by impact ionization are absorbed after moving a long distance, and therefore the effects of a source-body-tie structure may not be sufficiently attained under the recent demands for high-speed switching characteristics.
It is an object of the present invention to provide a semiconductor device including a MOS transistor having a source-body-tie structure that can effectively absorb holes generated by the impact ionization phenomenon, and a method for manufacturing the same.